that are cognitively meaningful, i.e., can be verified. This view has become known as the verifiability theory of cognitive meaningfulness.
Unfortunately, the verifiability criterion is too strong and rules out a lot of science. Consider again the claim that all ravens are black. We have seen earlier that to confirm this seems hopeless; verifying it is outright impossible, because you’d have to inspect all ravens past, present, and future. By the verifiability criterion for meaningfulness, the claim that all ravens are black is therefore meaningless. But that seems wrong. While “The absolute is beautiful” is rather obviously meaningless, “All ravens are black” is not. However, both are unverifiable. Thus, verifiability is the wrong criterion for distinguishing the meaningful from the meaningless.
Popper agreed with the positivists on the importance of distinguishing genuine science from pseudoscientific babble, but he didn’t think that taking a detour through a criterion for meaningfulness was the right approach. So he opted for falsification instead. “All ravens are black” can be falsified, while “The absolute is beautiful” can’t be. You can, in principle, find at a raven that’s not black, but you can’t find the absolute and see that it’s ugly. Thus, the first statement belongs to science, while the second one doesn’t, whether meaningful or not.
3.3.1 Progressive Modifications
However, we have also seen that due to the role of auxiliary hypotheses in theory testing, conclusive falsification is not possible either. A hypothesis can always be protected against falsification by denying one or more of the auxiliary hypotheses; in principle, one can even deny the observational statement with which the hypothesis has been found inconsistent. In the early 1800s, English chemist William Prout proposed that the atomic weights of the various elements are whole multiples of the atomic weight of hydrogen. It was well known though that some elements appear to have weights that are inconsistent with Prout’s hypothesis. Chlorine, for example, was measured to have 35.5 times the weight of hydrogen. Prout remained undeterred and suggested that the chemical processes used to isolate elements were defective, and thus the chlorine sample was impure. In this case, assuming the truth of the main hypothesis was used to criticize and consequently modify the then prevailing experimental techniques that produced observational statements.
This raises the question of how one should decide what to modify in light of an inconsistency between theory and observational statements: the main hypothesis, one or more of the auxiliary hypotheses, or the observational statements which are based on the experimental techniques producing them? As an answer, Popper proposed that any modifications made should increase the falsifiability of the resulting theory. Since falsifiability is a measure of content – the more falsifiers a theory has, the greater its content – this amounts to the advice to modify in the direction of greater content, by either being broader in scope or more precise.
As an example, consider the theory C that all orbits of celestial bodies are circular. This theory is of broader scope than the theory P that all orbits of planets are circular, since planets are a particular kind of celestial body. Having broader scope, it has more falsifiers. On the other hand, it is also more precise than the theory E that all orbits of celestial bodies are ellipses, because circles are a kind of ellipses. Thus, C has more content than both P and E – it has more content than P by being more universal, and it has more content than E by being more precise.
Popper claimed that modifications that increase a theory’s falsifiability contribute to the progress of science. The intuition behind this claim seems to be this: If we protect a theory from falsifications by modifying it in a nonfalsifiable way, scientific development comes to a stand still. Yes, the current theory has been protected from falsification, but at the expense of stagnation. It’s like going into the corner and pouting. Here’s a sports analogy. Suppose you have been beaten at your favorite sport. Sure, you can look for excuses – the referee was unfair, there was too much wind, the ball was rigged, etc. And since these things seem to be always happening, you won’t play anymore. But if that’s your reaction, you clearly won’t make progress. Maybe the better strategy is trying to improve your game and then compete as hard and as often as you can, which of course increases your opportunities of being beaten. If you then stay unbeaten in ever tougher competition, it seems like you’ve made progress, certainly more than you could have made by frowning in the corner and not playing again. Of course, even if you stay unbeaten for a long time doesn’t mean that you are a perfect player; there might still be better ones out there. But you have earned your right to play on for a while, to be kept on the team, as it were. And what goes for sports, Popper thinks, goes for theories. If we expose them to severe competition with other theories through tests, the ones that keep on winning earn their keep.
As mentioned earlier, Popper’s technical term for staying unfalsified through severe tests is being corroborated. The corroboration of a theory does not provide a reason for believing it to be true, or even probable to any degree. Rather, it means that it has survived varied and severe tests, where severity is a function of the number of potential falsifiers for a theory. Assigning corroboration is simply saying that the theory is consistent with a set of statements that are currently accepted as basic. Thus, the degree of corroboration of a theory can change with changes in bodies of accepted basic statements. It is therefore clearly not a sort of truth value, because the truth of a statement is not in this way relative to what other statements are accepted.
3.3.2 Basic Statements
What statements are accepted as basic at a given time? In contrast to the positivists, who thought they have found epistemically privileged statements in so-called protocol sentences, which allegedly describe the experiential bedrock for all of our theorizing, Popper thought that what statements are accepted as basic depends on the experimental context and can change over time. He did provide a list of considerations that should be involved in any decision process about basic statements. First, they must be easy to test. In Prout’s time, finding the atomic weights was thought to be easy. Second, they must be relevant to the theory undergoing testing. When Prout claimed that the weights of all elements are whole multiples of the weight of hydrogen, it was clear that a relevant basic statement is one about the weight of some element other than hydrogen. Third, we must keep in mind that their acceptance is provisional, and should the need arise, they too can be tested relative to other statements that are then accepted as basic for that purpose. The statement about chlorine was accepted as basic when it was used in an attempt to falsify Prout’s claim. But the experimental methodology eventually became the subject of testing itself when it was determined that the available procedures for purifying substances were imperfect. Testing the standard purification procedures required other statements to be accepted as basic. Thus, on Popper’s considered view, the process of falsification is a far cry from simply finding out that nature is in conflict with a hypothesis. Instead, it is embedded in a context of continuing criticism, where in principle nothing is exempt from criticism. There is no epistemic bedrock.
3.3.3 Moving and Burning
Popper’s conception of empirical science as a process of continual criticism of bold empirical conjectures has been attractive to many working scientists. But is his model of how science grows through criticism borne out by historical evidence? Let’s look at the Polish astronomer Nikolaus Copernicus’ reaction to the problem of stellar parallax and the British chemist Joseph Priestley’s introduction of negative weight.
Suppose you are in a driving car, approaching a city. You happen to look at two tall buildings far ahead on the right side of the road. One of them seems to be almost attached to the other, that’s how close they look to you. However, once your car is driving right past them, you notice that the two buildings are actually dozens of yards apart; of course, as the car continues on its way and you look back, the buildings seem to be closer together again. Something very similar should happen, if heliocentrism is true. As the earth moves
